Understand the DTMF in SIP Call

Overview

In SIP, there defines 3 types of DTMF: RFC2833, Inband, Info. You might doubt how to distinguish or check them.

How To

- RFC2833

We can check the DTMF directly in the VoIP Call Flow viewed by Wireshark. How to Analyze SIP Calls in Wireshark

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Select the RFC2833 RTP event to check the details. It's pretty straight forward.

If you output the audio, the RFC2833 RTP doesn't have any sound.

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- Inband

It is the actual sound of the DTMF. If you play RTP steams in Wireshark, you can see the DTMF wave.

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If need to check more wave details.

Firstly output the audio followed by this article: How to Output the SIP Call Audio for Wireshark Capture File

Then follow this article to check the DTMF wave: How to Check DTMF Wave?

 

- Info

It's a SIP packet. You can easily find out in the call flow view of Wirshark.

In the message body of the packet, you would see the digit information.

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